Genesis and activity of mo-based hydrotreating catalysts prepared by a sol-gel method

Molybdenum oxide-alumina catalysts used in hydrodesulfurization (HDS) with a wide range of Mo loadings (1–25% Mo) were prepared by the sol-gel process. Two different methods of adding the molybdenum oxide precursor to the support were used.In the first route, alumina is prepared by hydrolysis of aluminium tri sec-butylate in butanol and butanediol, and molybdenum is deposited by a classical dry impregnation with ammonium heptamolybdate (AHM). In the second route, the molybdenum oxospecies are dispersed in butanediol and added to the aluminium alkoxide before hydrolysis. The solids were calcined to obtain the oxide precursors which are then sulfided to give the active phase in hydrodesulfurization.The effect of preparation on the structural properties of alumina as well as on the state and dispersion of molybdenum in the dried, calcined and sulfided form was studied by various characterization techniques (XRD, XPS, Raman spectroscopy). Molybdenum appears to be present as well dispersed oxomolybdenum species in the oxide form even at high loadings. This good dispersion of molybdenum is preserved after sulfidation which induces the formation of MoS₂ crystallites whose morphology has been determined by HREM.The catalyst activities were evaluated in thiophene hydrodesulfurization and compared with that of catalysts prepared by dry impregnation of a commercial alumina. The observed performances are in agreement with the good dispersion of molybdenum at high loadings we were able to obtain owing to the sol-gel process.     

Influence of the nature of molybdenum compounds on the activity of Mo/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and NiMo/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> hydrotreating catalysts

The influence of the nature of molybdenum compounds on the catalytic activity of sulfided NiMo/γ-Al₂O₃ catalysts was studied. The samples were prepared by impregnating the support with mixed aqueous solutions of nickel nitrate and molybdenum-containing compounds: ammonium paramolybdate and the 6-series heteropoly compounds (HPCs) ammonium 6-molybdonickelate (NiMo₆-HPC) and ammonium 6-molybdoaluminate (AlMo₆-HPC). Complexing agents (tartaric acid or a solution of NH₃) were used for stabilizing mixed aqueous ammonium paramolybdate and nickel nitrate solutions and for simultaneously producing an acidic or alkaline medium. The starting molybdenum compounds and catalysts in the oxide form were characterized using IR spectroscopy and x-ray diffraction analysis. The activity of catalysts based on NiMo₆-HPC in the hydrogenolysis of thiophene and in the hydrotreating of the diesel fraction was higher than that of catalysts based on ammonium paramolybdate: at 320°C, the degree of sulfur removal from the diesel fraction was higher by 13–16% and the average degree of hydrogenation of polycyclic aromatic hydrocarbons was higher by 14–15%. It was also found that the use of AlMo₆-HPC does not cause such an effect.     

Acetalization of glycerol using mesoporous MoO3/SiO2 solid acid catalyst

Acetalization of glycerol with various aldehydes has been carried out using mesoporous MoO₃/SiO₂ as a solid acid catalyst. A series of MoO₃/SiO₂ catalysts with varying MoO₃ loadings (1–20 mol%) were prepared by sol–gel technique using ethyl silicate-40 and ammonium heptamolybdate as silica and molybdenum source respectively. The sol–gel derived samples were calcined at 500 °C and characterized using various physicochemical characterization techniques. The XRD of the calcined samples showed the formation of amorphous phase up to 10 mol% MoO₃ loading and at higher loading of crystalline α-MoO₃ on amorphous silica support. TEM analyses of the materials showed the uniform distribution of MoO₃ nanoparticles on amorphous silica support. Raman spectroscopy showed the formation of silicomolybdic acid at low Mo loading and a mixture of α-MoO₃ and polymolybdate species at high Mo loadings. Moreover the Raman spectra of intermediate loading samples also suggest the presence of β-MoO₃. Acetalization of glycerol with benzaldehyde was carried out using series of MoO₃/SiO₂ catalysts with varying MoO₃ loadings (1–20 mol%). Among the series, MoO₃/SiO₂ with 20 mol% MoO₃ loadings was found to be the most active catalyst in acetalization under mild conditions. Maximum conversion of benzaldehyde (72%) was obtained in 8 h at 100 °C with 60% selectivity for the six-membered acetal using 20% MoO₃/SiO₂. Interestingly with substituted benzaldehydes under same reaction conditions the conversion of aldehydes decreased with increase in selectivity for six-membered acetals. These results indicate the potential of this catalyst for the acetalization of glycerol for an environmentally benign process.     

Macroporous 3D carbon-nitrogen (CN) confined MoOx catalyst for enhanced oxidative desulfurization of dibenzothiophene

Macroporous 3D carbon doped with nitrogen confined Mo catalyst (MoO_x@CN) had been prepared by a facile one-step pyrolysis technique using silica as a template and was employed for oxidative desulfurization (ODS) of dibenzothiophene (DBT) in model fuel with H₂O₂ as oxidant. The effect of different operating conditions (i.e., reaction temperature and time, catalyst dosage, H₂O₂/DBT (O/S) molar ratio) were also systematic investigated. Under the optimal reaction condition, MoO_x@CN catalyst exhibited highly excellent ODS performance toward DBT, the highest sulfur removal efficiency can be up to 99.9% and sulfur content was wiped out from 800 ppm to 10 ppm. Due to the robust 3D structure promoting rapid transfer, in addition to the increased number of active sites induced by the Mo vacancies, the catalyst, prepared using chitosan and ammonium heptamolybdate in a mass ratio of 1:0.5, displayed rapid kinetics and low activation energy in the oxidation of dibenzothiophene. Moreover, it exhibited excellent recyclability after five cycles without any obvious decrease in catalytic activity for the oxidative desulfurization reaction.     

二钼酸铵晶体饱和水溶液Raman光谱的变异现象及其机理

记录了常温下二钼酸铵晶体饱和水溶液的Raman光谱，并分别与二钼酸铵晶体、仲钼酸铵晶体、仲钼酸铵晶体饱和水溶液、水溶液状态下单钼酸根离子的Raman光谱进行了比较研究。结果表明：二钼酸铵晶体饱和水溶液Raman光谱相对二钼酸铵晶体Raman光谱，明显地发生了变异现象。二钼酸铵晶体饱和水溶液Raman光谱其主要特征峰最高振动频率937.6 cm^-1与仲钼酸铵晶体饱和水溶液Raman光谱主要特征峰最高振动频率937.6 cm^-1完全吻合，而其次高振动频率893.9 cm^-1，恰好介于水溶液中单钼酸根离子Raman光谱主要特征峰最高振动频率895.1 cm^-1与仲钼酸铵晶体饱和水溶液Raman光谱主要特征次高峰振动频率891.0 cm^-1之间，而且三者彼此接近。二钼酸铵晶体饱和水溶液Raman光谱主、次特征峰强度之比值为2.1，与仲钼酸铵晶体饱和水溶液Raman光谱主、次特征峰强度之比值4.4相比，一半不足。提出了一种利用Raman光谱主要特征峰振动频率及其主、次特征峰强度之比值对二钼酸铵晶体饱和水溶液组分同时进行定性和半定量分析的新方法。发现了常温下二钼酸铵晶体饱和水溶液中二钼酸根离子Mo₂O₇^2-已经不复存在，完全转变成了优势组分仲钼酸根离子Mo₇O₂₄^6-和次要组分单钼酸根离子MoO₄^2-；证明了常温下含钼水溶液酸化过程中溶液Raman光谱离散性变化现象的存在。运用结构化学和物理化学原理同时讨论了二钼酸铵晶体饱和水溶液Raman光谱发生变异现象的机理。     

Effect of Mo loading on transesterification activities of MoO3/γ-Al2O3 catalysts prepared by conventional and slurry impregnation methods

Summary The effect of Mo loadings and preparation methods, slurry and conventional impregnation, on the performances of alumina-supported MoO₃ catalysts in transesterification of dimethyl oxalate (DMO) with phenol was investigated. Slurry prepared MoO₃/-Al₂O₃ catalyst exhibited higher activity and dispersion capacity than conventional one. Slurry MoO₃/water was used instead of an ammonium heptamolybdate solution. Highly dispersed amorphous Mo catalysts were obtained, closely related to the catalytic activities without calcination, waste solutions, and calcining nitrogenous gases.     

硫代硫酸铵预硫化的Mo/AC催化剂加氢脱硫性能的研究

采用等体积浸渍法将硫代硫酸铵(ATS)负载在Mo/AC催化剂上,制备了器外预硫化的Mo/AC-ATS催化剂;以噻吩加氢脱硫(HDS)为探针反应,考察了活化温度和活化时间对预硫化催化剂加氢脱硫活性的影响。研究发现,300 ℃下活化0.5 h所得到的预硫化催化剂具有最好的加氢脱硫活性。与传统硫化剂CS₂和DMDS硫化的催化剂相比,采用Mo/AC-ATS催化剂,在最佳活化条件下,噻吩转化率分别提高了34%和42%。XPS、TPR-MS和TEM等表征结果显示,预硫化的Mo/AC-ATS催化剂中Mo⁴⁺含量较高,这是其具有较高加氢脱硫活性的主要原因。     

Unsupported Molybdenum and Cobalt-Molybdenum Nitrides for Thiophene Hydrodesulfurization

The catalytic activity and the structure of unsupported Mo and CoMo nitrided catalysts were investigated. It was found that the structure and catalytic activity of the nitrided catalysts are influenced by the conditions of nitridation. Molybdenum oxynitrides are more active in hydrodesulfurization (HDS) of thiophene than MoS₂. The addition of cobalt to nitrided Mo improves its HDS activity, however, sulfided CoMo catalyst is still more active than the nitrided one. Synergy between Co and Mo for the nitrided unsupported CoMo catalyst exists at lower degree than for the sulfided form of CoMo.     

钼催化剂上甲醇直接气相羰基化活性与吸附的关系

 制备了一系列非负载的钼催化剂，考察了催化剂上甲醇直接气相\r\n羰化活性与反应物及产物吸附的关系．结果发现，催化剂的制备方法对\r\n甲醇直接气相羰化活性的影响很明显，以纯二硫化钼试剂制备的催化剂\r\n，甲醇转化率与羰化产物乙酸甲酯的选择性最低；以三氧化钼气相还原\r\n硫化制备的催化剂，其羰化活性较低；以钼酸铵溶液经硫化铵溶液或硫\r\n化氢气体硫化制得的催化剂，其性能明显优于前两种，尤以钼酸铵经硫\r\n化铵溶液硫化制得的催化剂的性能最佳．催化剂的羰化活性明显依赖于\r\n催化剂的吸附性能，羰化活性高的催化剂不仅吸附CO的量大，而且对甲\r\n醇和乙酸甲酯的吸附量也明显较大．     

Fluoride modification of Mo/Al2O3 catalysts: Characterization of the changes induced in support and Mo phases

The characterization of fluoride-modified Mo/Al₂O₃ catalysts was performed in order to investigate on the effect that low levels of fluoridation of the alumina support (0-2.0 wt.%) cause on the support itself and on the supported Mo oxide and sulfide phases. Fluoride-modified Al₂O₃ supports and Mo/Al₂O₃ catalysts where characterized by nitrogen physisorption, scanning electronic microscopy (SEM-EDX), isoelectric point (IEP), Fourier transform infrared spectroscopy (FT-IR), infrared spectroscopy of adsorbed CO₂ (IR-CO₂), and temperature programmed reduction (TPR). The dispersion of the sulfided catalysts was estimated by dynamic NO chemisorption. The results indicate that the different hydroxyl types present on the alumina surface react to a different extent with fluoride and that it is the most basic hydroxyl groups that are titrated first.The consumption of the alumina OH by F⁻, inhibits, during the deposition of Mo, the formation of tetrahedral molybdenum oxide species in strong interaction with the support, leading to an increased number of polymeric octahedral Mo surface species. The NO adsorption results put in evidence a drop in the dispersion of the MoS₂ phase present in the sulfided samples.     

Cyclohexane oxidation with an O<Subscript>2</Subscript>–H<Subscript>2</Subscript> mixture in the presence of a two-component Pt/C–heteropoly acid catalyst and ionic liquids

Approaches to increase the efficiency of Pt/C–heteropoly acid catalyst in a liquid-phase oxidation of cyclohexane using an O₂–H₂ mixture were studied. It was shown that small additives of ionic liquid (BMImBr, Bu₄NBr, or Bu₄NHSO₄) significantly improve the catalytic effect of the Pt/C–H₃PMo₁₂O₄₀–CH₃CN system at 35°C, by slowing the rate of side reactions resulting in water formation, increasing the rate of oxygenate formation, and inhibiting their secondary oxidation reactions. The efficiency of H₂ consumption increases from 2 to 18–25%, while the selectivity of cyclohexane conversion is 92–98%. The substitution of one or two Mo(VI) ions by V(V) in the structure of the heteropoly acid decreases these parameters. In the presence of Bu₄NHSO₄, a Pt/C catalyst can be used many times. During the reaction, the heteropoly acid present in the solution is in a reduced state under the action of the reaction medium and undergoes reversible redox transformations. The nature of the catalytic action of the studied system is explained from the viewpoint of the effect of ionic liquids on the properties of a Pt/C catalyst in activating O₂, heteropoly molybdate chemistry, and the known mechanisms of the peroxide oxidation of hydrocarbons.     

Mesoporous silica-supported V-substituted heteropoly acid for efficient selective conversion of glycerol to formic acid

V-substituted polymolybdenum phosphoric acid (PV_xMo) supported on mesoporous silica was prepared and investigated as a catalyst for the oxidation of glycerol to formic acid in a batch operation. Different synthetic methods for PV_xMo supported on mesoporous silica were compared. Detailed characterizations of the final products were carried out by N₂ adsorption and desorption, XRD, HR-TEM, SEM, ICP-OES, XANES, NH₃-TPD, and FTIR to identify the chemical properties and the porous structure of silica-supported PV_xMo, as well as the strong interactions between PV_xMo with the silica skeleton. These critical properties explain the bifunctionality of silica-supported PV_xMo as a catalyst for the selective oxidation of glycerol to formic acid with standing stability.     

Flow injection method for antimony(III) based on its enhancement of the molybdenum blue reaction

A simple flow-injection methodology is described for the determination of antimony using spectrophotometric detection. The method is based on the enhancing effect of antimony in the molybdenum blue reaction. Phosphate and heptamolybdate reagents are premixed and pumped as a reagent stream, into which the antimony sample is injected. This allows the formation of a mixed heteropoly complex, which is then rapidly reduced by ascorbic acid to form the intense blue complex, the absorbance of which is monitored at 660 nm. A continuous-flow procedure is used and 120 samples can be processed per hour. The measurement range is 0–100 mg l^?1 antimony, with a detection limit of 0.5 mg l^?1. The relative standard deviation is 0.65–2.1% in the range 20–5 mg l^?1. Arsenic and silica cause interferences of ?4% and +4.6%, respectively, when present at concentration equal to that of the antimony.     

Deep oxidative desulfurization of fuels catalyzed by molybdovanadophosphoric acid on amino-functionalized SBA-15 using hydrogen peroxide as oxidant

This study reports the usage of molybdovanadophosphoric acid catalyst on amino-functionalized SBA-15(PMoV₂/SBA-15-NH₂) for the removal of sulfur from model oil (dibenzothiophene dissolved in n-hexane). To increase the tendency for adsorption of heteropoly acids, mesoporous SBA-15 silica was functionalized with amino groups by postsynthesis grafting, using 3-aminopropyltrimethoxy silane as the coupling agent. Immobilization of molybdovanadophosphoric acid on pure SBA-15 (PMoV₂/SBA-15) was also studied for comparison and the catalysts were characterized by physicochemical and spectroscopic methods. It was found that the catalysts exhibit high catalytic activities and PMoV₂/SBA-15-NH₂ is more durable than PMoV₂ impregnated on unmodified mesoporous SBA-15 silica. The results may bring about improvement for oxidative desulfurization of transportation fuels.     

Mechanochemical synthesis of nanocrystalline nickel-molybdenum compounds and their morphology and application in catalysis: II. Effect of mechanochemical activation parameters—process power density and exposure time—on the composition and structure of nickel-molybdenum compounds

The effect of mechanochemical activation parameters-process power density and the time of treatment of a mixture of nickel hydroxocarbonate NiCO₃ · 2Ni(OH)₂ · nH₂O and ammonium paramolybdate (NH₄)₆Mo₇O₂₄ · 4H₂O -on the phase composition, specific surface area, and morphology of mechanically activated products at different Ni: Mo atomic ratios was studied. It was found that, at a mechanochemical activation process power density of 6.2 W/g, layered transition metal molybdates (LTM compounds) with different amounts of crystal water were the constituents of the products, whereas the products mechanically activated at a power density of 28.0 W/g contained a mixture of LTM compounds and heteropoly compounds with the Anderson structure regardless of activation time.     

Study of silica-supported heteropoly acids by microcalorimetry

Silica-supported heteropoly acids have been studied by microcalorimetry. The results are greatly dependent on both the activation temperature and the heteropoly acid, in agreement with the n-hexane cracking experiments. It is shown that very strong acid sites are formed on H₄SiW₁₂O₄₀/SiO₂ activated at 623 K and on H₃PW₁₂O₄₀/SiO₂ activated at 423 K.     

Formation and reduction of molybdothorophosphoric acid

The stoichiometry of formation and the kinetics of reduction of molybdothorophosphoric acid in nitric acid solutions were studied spectrophotometrically. The Mo:Th:P ratio in the complex is 12:1:1, assuming that Mo(VI) exists in acid solutions as a dimer. The ternary heteropoly acid is more stable and is reduced more slowly to the heteropoly blue than 12-molybdophosphoric acid. The kinetics of the first stages of the reduction were studied with ascorbic acid and p-methylaminophenol as reductants. The experimental rate law is in good agreement with a mechanism involving an equilibrium step in formation of the heteropoly acid followed by the reduction. Under recommended conditions, Beer's law was obeyed up to 40 mg l^?1 thorium.     

Quantitative and qualitative studies of silica in different rice samples grown in north of Iran using UV-vis, XRD and IR spectroscopy techniques

Silicon is an essential trace element and is found in vegetables, fruits, cereals, water, pasta and rice (Oryza sativa). In this work, the silica content of different types of rice grains were measured. Here, we used the heteropoly blue photometric method with a double beam UV-vis spectrophotometer to determine the amount of silicon in rice samples (n = 7) that were collected in the north of Iran. The samples were digested with wet-ashing method by microwave-assisted heating and then treated with ammonium molybdate to produce a yellow color compound in acidic solution (ca. pH 1.2) and then reduced to give a heteropoly compound with a blue color. Analyses were performed using standard addition method and absorbance values were measured with double beam UV-vis spectrophotometer at λ_max = 815 nm. Results indicated that the silica content was 307-451 mg/kg for the samples. X-ray diffraction patterns and infra-red spectra were obtained from rice samples without any sample treatment.     

Study of oxidic and sulfided selective hydrodesulfurization catalysts for gasoline using Raman spectroscopy

A series of CoMo/Al2O3 catalysts for selective hydrodesulfurization （HDS） of gasoline were studied with Raman spectroscopy, a powerful method that creates specific signals for the states and the distributions of oxidic precursors and sulfided active phases. The higher the Mo and Co, the lower the tetrahedrally coordinated molybdate, and the higher the polymolybdate. But the amount of polymolybdate decreased when CoMoO4 appeared. Cobalt-promoted polymolybdate was the precursor, and its relative content correlated well with the HDS selectivity. For sulfided catalysts, adding the cobalt-promoter led to local distortion-disorder of the MoS2 structure and the formation of a CoMoS phase. This method can provide important information for designing new industrial selective-HDS catalvsts.     

SiW(12)/Al2O3的硫化与加氢脱氮活性

为对ＳｉＮｉ（Ｃｏ）Ｗ１１（Ｍｏ１１）双金属Ｋｅｇｇｉｎ型杂多酸作为模型前身物，载于Ａｌ２Ｏ３上应用于加氢精制催化剂活性相的研究提供依据和参考，本文研究了ＳｉＷ１２在Ａｌ２Ｏ３上的分散状态，硫化行为及其加氢脱氮活性，用吸附法和浸渍法均可将ＳｉＷ１２稳定和高分散地担载于Ａｌ２Ｏ３表面上，在Ａｌ２Ｏ３载体上，ＳｉＷ１２的硫化反应发生在５７３～６７３Ｋ狭窄温度范围内，该硫化作用起始于其Ｋｅｇｇｉｎ结构破